For the sake of your future child, don't smoke. Be wary of alcohol. Eat for three: yourself, your unborn baby, and your spouse.

And try to get your wife to follow the same healthy lifestyle. While humanity has long known that toxicants can undermine male fertility, common thinking was that the postconception health of the fetus was solely the province of the mother. It turns out that the health habits of both parents can affect the odds not only for conception but for miscarriage, birth defects, and childhood cancer. New research confirms that potential medical problems for offspring can ride sperm from the father all the way into the egg.

In fact, findings suggest that men who wish one day to sire healthy offspring should start thinking more like a savvy pregnant woman. Though the pregnancy-related warnings on wine labels and cigarette packs target women only, healthy pregnancies involve the teamwork of a relay race, and before conception the future father has a turn carrying the baton.

The Taboo Question

A 29-year-old Boston woman (some identifying characteristics and information about this couple have been changed) couldn't understand why she had suffered two miscarriages. Her gynecologist had run a battery of tests and found nothing wrong with her. That's when she began to consider a question women rarely ask: Is it possible my husband can't have healthy children?

Her husband, 40, didn't want to come to the office of Marc Goldstein, M.D., professor of urology and the director of the Center for Male Reproductive Medicine and Microsurgery at the New York Hospital-Cornell Medical Center, and was angry when they arrived. And when Dr. Goldstein offered a possible solution to the mystery of her miscarriages, he says, "she was angry at her husband and he was angry at me."

The husband was a construction worker and routinely involved in the demolition of old buildings that had lead pipe or lead-based paint. "That was a possible clue," says Dr. Goldstein. A man's exposure to lead has been associated with his partner's miscarriages. "He was also a heavy drinker -- a six-pack every night," Dr. Goldstein says. Clue two: Animal studies raise questions, still largely unanswered in humans, about the longest and most painful kind of hangover: damage to the fetus caused by a father-to-be's excessive alcohol consumption. And the man had smoked two packs a day for 25 years, since he was 15, a third hint of danger. Recent studies with human subjects suggest that male smoking can harm sperm, causing miscarriage and passing on a slight but significant legacy of cancer to offspring, even if the mother doesn't smoke.

But what evidence was there that the man's bad health habits had caused these particular pregnancy failures? It was circumstantial but compelling, and "something he had never told his wife before," Dr. Goldstein says. "His previous wife had miscarried twice." If there was something wrong with her, the problem seemed to disappear after their divorce. "When his first wife got married again," Dr. Goldstein says, "she went on to have healthy children with her next husband."

Miscarriages happen to at least one of every five pregnant women. In some cases, these "spontaneous abortions" are nature's way of ending a pregnancy likely to lead to a baby born with serious malformations. They can also be a sign that the mother's womb is inhospitable to fetal growth. In the case of the Boston woman, doctors had already ruled out typical causes. So Dr. Goldstein narrowed in on how her husband might have triggered the pregnancy problems.

Tests of the man's blood revealed lead levels within a normal range, so that didn't appear to be the culprit. But when the man's sperm were examined under a microscope, they were clearly misshapen. Some had two tails. Some had irregularly shaped heads. Research shows that smoking and drinking alcohol both can distort sperm's form. And abnormally shaped sperm is associated with a higher than average incidence of miscarriage.

Drugs and alcohol aren't the only cause of abnormal sperm shapes. Varicocele, for example, a painless swelling in the scrotum from varicose (enlarged) veins, can lead to a distinctive narrowing of the sperm. In itself, varicocele isn't a serious disorder. But it can contribute to infertility and, experts say, the narrowing can be associated in some cases with miscarriage -- most likely if the man uses drugs or smokes cigarettes. That means a man with varicocele who drinks to excess or smokes increases the risk of disrupting his wife's pregnancy.

"It's true that misshapen sperm are less likely to succeed in fertilizing an egg," Dr. Goldstein acknowledges. "But if they do, the fetus is more likely to have problems and the odds of miscarriage go up." His prescription to his alcoholic and cigarette-puffing patient was a strong suggestion that he join Alcoholics Anonymous to help curtail his drinking and buy a nicotine patch to assist in weaning him of his cigarette addiction.

"He quit smoking and got into AA," Dr. Goldstein says. Six months later, the couple hadn't yet conceived. But the shape of the sperm had significantly improved -- they had a classic bulbous head and long, thin tail -- increasing the odds that his better health might spawn a successful pregnancy. And eventually it did: A few months after that, the woman became pregnant, and last May the couple became the proud parents of a healthy baby.

"All the eggs a woman will ever have are created when she is a fetus inside her mother," says Bruce Ames, Ph.D., professor of biochemistry and molecular biology at the University of California, Berkeley. Sperm cells, by contrast, are produced continuously through cell division all during a man's adult life. At every cell division, the sperm are at risk of mutation -- a small change that can mean a big problem for the man's children. That's why, Ames argues, "fathers ultimately contribute more to the risk of gene mutations than mothers."

So where does that leave a concerned dad-to-be? Doctors suggest three strategies for producing safer and healthier sperm:

Quit Smoking

And do so as long before conception as possible. Perhaps years before. That's the conclusion of a new study that solves what has for years been a major puzzle about smoking and pregnancy: In a family where both parents smoke, how can doctors say which parent contributed to any medical problems in their children? Although further studies need to be done, the research by Bu-Tian Ji, M.D., who is also a Ph.D. candidate at the National Cancer Institute (NCI), suggests that men ought to quit smoking to protect their children from childhood cancer.

Dr. Ji went back home to his native China for his research because many more Chinese men smoke than women. "The smoking rate in Shanghai is about 60 percent among men," Dr. Ji says. "But traditionally, Chinese women don't smoke or drink." That means Dr. Ji and other researchers could easily zero in on large numbers of families where the dad smokes and mom doesn't.

Dr. Ji and his team of scientists studied 642 cases of cancer in Chinese children under the age of 15. At the same time they looked at another similar group with no cancer history, for comparison. They then confirmed the smoking histories of both parents to isolate what happens to the next generation when it's the man who uses tobacco.

What they found: Fathers who had smoked cigarettes at any point in their lives were 30 percent more likely to have a child with cancer than dads who had never smoked. "The length of time they smoked turned out to be more important than how many cigarettes they lit up per day," Dr. Ji says.

Dr. Ji's not sure why a man's past smoking habit seems to put his child at greater risk. "Even though sperm are made fresh in a man's body, we think maybe the environment in the reproductive system can continue to damage the sperm, or not protect it," he says. "But we don't yet have proof that this is what happens."

He acknowledges that his study doesn't exclude the possibility that the increase in childhood cancer is caused by secondhand smoke, inhaled by mothers-in-waiting. But other studies, of mothers who smoke, find no effect on the rate of cancer in their kids. That suggests that sperm, not secondhand smoke, could be the culprit. Another 1997 study, in England, backs up Dr. Ji's major finding. It links a father's smoking habit -- but not a mother's -- to an increased risk of cancer death among children in the U.K.

Dr. Ji looked only at the effects on childhood cancer, diagnosed annually in about 14 of every 100,000 U.S. children under age 15. Several other studies dating back to the 1960s reveal that fetuses and newborns are more likely to struggle for their lives if their fathers smoke. One showed that the overall death rate among infants of fathers who puff cigarettes was about 45 percent higher than the toll for babies sired by nonsmoking fathers. In addition, almost all studies of fathers who smoke find a greater incidence of birth defects in their children than in the offspring of fathers who don't light up.

More research is needed before anyone can be sure of the cancer connection and the overall risk of genetic damage to the next generation. Still, Dr. Ji's advice to men is not to wait until all the results are in. Stop smoking as long as possible before conception, he says. "I believe that it's best to quit at least five years before."

Eat As Though You Were Pregnant

If expectant mothers eat for two, their husbands ought to eat for three before conception: themselves, their partners, and their children-to-be. So it appears to Bruce Ames, who investigated the reproductive health of volunteers in a United States Department of Agriculture (USDA) study of low-vitamin diets.

"The USDA has a human nutrition lab where they observe volunteers eating a specific diet for four months at a time," he says. So he asked if he could study some sperm from a group of men on a regimen low in vitamin C. They were getting about ten milligrams a day, one-sixth of the current recommended allowance.

It was already known that vitamin C appears to be important to male reproductive health. "There's about eight times as much of it in seminal fluid, the river in which sperm ride, as there is in blood plasma," Ames says, suggesting that C plays some central role in promoting conception.

When he got the sperm samples, Ames found that the sperm from the C-deprived volunteers was two and a half times as likely to be damaged as that from men who got enough of the vitamin. So vitamin C in the male reproductive system appears to play the role of palace guard.

Against what? Ames theorizes that the threat to sperm comes from toxins called free radicals, which are produced in the body. Cigarette smoke, radiation, exhaust fumes, and even excessive sunlight accelerate their production.

The body can repel the free radical assault with a diet high in antioxidants such as vitamins C and E. If you don't get enough of the protective vitamins, Ames says, "you wind up with injuries to the chromosomes in the sperm cells." The result is like randomly rewriting portions of the sperm's instructions for making a new life. While most of the damaged cells are repaired naturally by the body, some injuries result in a mutation when a cell divides. "And that may lead to trouble in the next generation," Ames argues. Susan Kleiner, Ph.D., a nutrition consultant in Seattle agrees, at least in theory. "We know that sperm can carry genetic mutations to the egg," she says. "So why couldn't sperm damaged from poor diet or tobacco also carry mutations?"

Kleiner recommends that would-be fathers pay more attention to nutrition, and specifically:

Eat at least three to five servings of vegetables and two to four servings of fruit every day to get enough vitamin C and beta-carotene, both antioxidants.

Increase consumption of seeds, nuts, and wheat germ to get enough of a third free radical fighter, vitamin E.

Toss in green vegetables like broccoli, collard greens, kale, romaine lettuce, and Swiss chard -- all great sources of folic acid, which Kleiner says might be as important to men as women for healthy conception. If this turns you off, eat more dried beans, peas, peanuts, sunflower seeds, whole grains, and oranges, other foods yielding folic acid as well as a healthy variety of nutrients and fiber.

Consider taking a multivitamin if your diet is low on these foods. But choose a moderate dose over mega-vitamin therapy.

Drink Moderately

Since 1989, labels on beer and other alcoholic beverages have warned pregnant women of risks to the fetus posed by drinking. Research suggests that men who are contemplating fatherhood ought to precede their partners into sobriety.

In a series of experiments by Theodore Cicero, Ph.D., professor of neuropharmacology at the Washington University School of Medicine, in St. Louis, young rats got high doses of alcohol early in their lives. Then they were put on an alcohol-free regimen for two to three weeks and bred with females. The rat mothers had modestly smaller litters, but the birth weights of the offspring were normal. The early binging by male rats at first seemed to have no discernable effect on their babies' physical well being.

But when Cicero looked into how these young rats developed, he found "subtle differences" compared with alcohol-free rats. "Male alcohol-sired offspring had significantly lower levels of testosterone," Cicero says. They did badly on several tests requiring them to learn to navigate mazes. And females born of the once-inebriated animals had abnormal levels of stress hormones. The results, Cicero says, are "highly consistent" with observations of human kids with alcoholic fathers. In general, the children are "not grossly malformed or impaired, but have some pronounced selective intellectual and functional deficits." The news in his work is that a man's early exposure to alcohol may later affect his children, even if he quit drinking before conception.

No one knows exactly what significance the rat research has for human fathers. "Such studies are like sentinels," says Ernest Abel, Ph.D., a professor of obstetrics and gynecology at Wayne State University. "They give you a suggestion that, at the human level, something needs to be looked at, and we should not ignore it. But these are not definitive in any way." Taken all together, though, this and other alcohol studies support some common sense: Think twice before you belly up to the bar and order a double while trying to conceive.

We can't ensure that our children will inherit our best personality traits, hair color, or smile. But men can probably do a lot, long before they even become fathers, to make sure their kids aren't put at risk by their own youthful excesses.